This invention relates to resin systems particularly adapted for use as corrosion-resistant coatings on a wide variety of materials or substrates.
Homopolymers of furfuryl alcohol are known to be excellent for use as corrosion-resistant coatings having, when cured, a wide range of chemical resistance such as renders them suitable for service in non-oxidizing acids, alkalies, salts, gases, oils, greases, detergents and most solvents at temperatures up to 375.degree. F.
The principal drawbacks of such coatings are that they are brittle, do not adhere to steel, aluminum, copper or any other metal, and cannot be used on alkaline materials, such as concrete, due to the requirement for acidic curing agents in connection with these resins. As a result, coatings and cements based on homopolymer of furfuryl alcohol are restricted in use principally to wood and ceramic materials.
Another drawback of acid cured homopolymers of furfuryl alcohol is the high degree of shrinkage and high porosity incidental to the loss of water as by-product of the condensation reaction during cure. However, despite the above limitations, furfuryl alcohol homopolymers when cured have considerable commercial importance as corrosion-resistant coatings and cement.
Epoxy resins, on the other hand, are noted for their low shrinkage during cure, since epoxy resins react with very little rearrangement and ordinarily with no volatile by-products being evolved. Also, unlike the above mentioned homopolymers of furfuryl alcohol, epoxy resins may be cured with a wide range of agents including acid curing agents such as carboxylic acid anhydrides, dibasic organic acids, phenols and Lewis acids, and basic curing agents such as Lewis bases, inorganic bases, primary and secondary amines and amides. Epoxy resins, due also to their low shrinkage during cure, are capable of strongly adhering to virtually any substrate.
Epoxy polymers, when cured, also exhibit reasonable chemical resistance. Because of the carbon-to-carbon or ether linkages within the epoxy resin molecule, these resins are extremely stable to the reaction of alkalies and have reasonable resistance to most acids and many solvents. Generally speaking, the chemical resistance is dependent upon the curing agent and the degree of cure.
However, cured epoxy resins are inferior to cured homopolymers of furfuryl alcohol in regard to chemical resistance and to high temperature resistance. In regard to the latter, cured epoxy resins tend to become brittle at high temperatures.